Light-emitting device, display device, and stress sensor

ABSTRACT

A stacked structure ( 1 ) includes an electrostriction layer ( 2 ) including an electric inductive distortion material and a stress light-emitting layer ( 3 ) including a stress light-emitting material. When applying a voltage to the electrostriction layer ( 2 ) in the stacked structure ( 1 ), the electric inductive distortion material deforms, thereby the electrostriction layer ( 2 ) deforms. The deformation of the electrostriction layer ( 2 ) causes an external force to act on the stress light-emitting material of the stress light-emitting layer ( 3 ), and the stress light-emitting layer ( 3 ) emits light, accordingly. That is, by applying the voltage to the stacked structure ( 1 ), the stacked structure ( 1 ) can emit the light.

This application is a 371 of PCT international application Ser. No.PCT/JP03/03230, filed on Mar. 18, 2003.

TECHNICAL FIELD

The present invention relates to a novel light-emitting device, adisplay device, and a stress sensor, which emit light in response to adeformation due to an externally applied voltage.

BACKGROUND ART

Conventionally used as a typical light-emitting device are a lightemitting diode (LED), a vacuum fluorescent display (VFD), a fluorescentlamp, an incandescent lamp, or the like.

In a field of a display using LED (serving as the light-emittingdevice), an LED which emits blue light has been developed. Since red,green, and blue LEDs have been lined up, it is possible to carry out afull-color display. Thousands of three-color LEDs are provided in mostof existing supersized full-color screens.

In addition, used as another existing displays are a CRT (Cathode-RayTube) display, a plasma display, a liquid crystal display, or the like.

The CRT display usually has three electron guns built-in. Three electronbeams shot by the three electron guns are directed to a face glass ofthe display, and causes fluorescent materials, which are applied on aback surface of the face glass, to emit light. This allows the CRTdisplay to carry out an image display. Moreover, basically, each pixelin the plasma display is partitioned by partition walls. Mercury argongas, xenon gas, or the like is sealed within each partitioned pixel.That is, it is possible to say that thousands of extremely smallfluorescent tubes are provided within a panel of the plasma display.

The liquid crystal display is basically arranged so as to include twoglass plates, and a liquid crystal layer provided between the two glassplates. The liquid crystal layer is made by pouring liquid crystal in agap between the two glass plates. The liquid crystal display carries outthe image display by applying a voltage across the liquid crystal layersandwiched between the two glass plates so that transmittance of theliquid crystal layer is controlled.

By the way, conventionally, a strain gage is mainly used as a stresssensor which measures stress exerted on architectural structures, or thelike. The strain gage measures the strain by utilizing a physicalphenomenon in which a resistance value of an electric resistor changesin response to the strain applied to the electric resistor.

However, the conventional light-emitting devices such as the fluorescentlamp, the vacuum fluorescent display, or the incandescent lamprespectively have the following problems.

That is, since the fluorescent lamp uses mercury, it is impossible toavoid environmental problems. Moreover, the vacuum fluorescent displayhas a triode vacuum tube structure composed of a positive electrode,negative electrode, and a grid, thereby giving rise to the complexity ofthe structure. Furthermore, since the incandescent lamp emits the lightbased on a heat emission obtained by heating up a filament in a glassbulb, the incandescent lamp has a short life span and has lowcrashworthiness.

The displays using the conventional light-emitting device have thefollowing problems.

Namely, in the case where the LED is used as the light-emitting sourceof the full-color screen, the image display on the screen is carried outby thousands of dot emissions. That is, the image displayed on thescreen is an aggregate of light-emitting dots. As such, it is difficultto improve a quality of the image displayed.

Moreover, since the CRT display structurally requires a glass tubehermetically sealed under high vacuum, it is complex in structure, itbecomes large in volume, and it is impossible to save weight. Inaddition, another problems arise that the crashworthiness is low andthere is a high possibility that the CRT display is destroyed by heat.

Furthermore, some plasma display uses mercury gas, thereby giving riseto a problem relating to environmental protection. Moreover, since theliquid crystal display uses the fluorescent tube as the light-emittingsource, it has a problem relating to environmental protection like theplasma display does.

Moreover, the strain gage serving as a conventional stress sensor hasthe following problem. That is, a single strain gage can measure thestress only at a specific point of measuring object. In order to measurea stress distribution state of the measuring object, a plurality ofstrain gages are required. This is the problem which the strain gagehas.

By the way, Japanese unexamined patent publication No. 49251/2001(Tokukai 2001-49251, published on Feb. 20, 2001) has proposed a novelstress light-emitting material which emits the light in response to adeformation due to mechanically applied external force. The presentinventors have attempted to utilize the stress light-emitting materialto solve the conventional problems.

DISCLOSURE OF INVENTION

The present invention was made in view of the foregoing conventionalproblems, and an object of the present invention is to provide alight-emitting device which is pollution-free, longer lasting, easy toproduce, simple in structure, and strong. Moreover, another object ofthe present invention is to provide a display device which has a highimage quality, high crashworthy and high heat resistance, and ispollution-free. Furthermore, a further object of the present inventionis to provide a stress sensor which can easily measure a stressdistribution state of measuring object.

To solve the above problems, a light-emitting device of the presentinvention includes (i) an electrostriction section including an electricinductive distortion material which deforms in response to an appliedvoltage, and (ii) a stress light-emitting section including a stresslight-emitting material which emits light in response to externallyapplied force.

With the arrangement, since the electrostriction section includes theelectric inductive distortion material, the electrostriction sectiondeforms in response to the applied voltage. By propagating thedeformation of the electrostriction section to the stress light-emittingmaterial, the external force acts on the stress light-emitting material.This allows the stress light-emitting material to emit the light. Thatis, the light-emitting section can emit the light. Note that, the stresslight-emitting material utilizes the nature in which the electronsexcited by the mechanical energy carries out luminescence when theelectrons thus excited move back toward the ground state. Moreover, whenan AC voltage is applied to the electric inductive distortion material,the electric inductive distortion material vibrates in response to afrequency of the AC voltage thus applied. The stress light-emittingsection may periodically emit the light in response to the periodicalvibration.

Moreover, the electric inductive distortion material and the stresslight-emitting material can be formed without using materials, whichcause environmental problems, such as mercury which is used in aconventional fluorescent lamp. As such, the electric inductivedistortion material and the stress light-emitting material will nevercause any environmental problems. Moreover, the light-emitting device ofthe present invention has a two-section structure of theelectrostriction section and the stress light-emitting section.Therefore, as compared with a conventional fluorescent character displaytube, the light-emitting device of the present invention has a simplerand stronger structure, and is easily manufactured.

Furthermore, unlike the conventional incandescent lamp which emits thelight based on the heat emission, the light-emitting device of thepresent invention emits the light by utilizing the nature in which theelectrons excited by the mechanical energy carries out luminescence whenthe electrons thus excited move back toward the ground state. As such,the light-emitting device does not bring about the heat rise caused bythe light emission. That is, the light-emitting device of the presentinvention can last long, have good luminous efficiency, and is compactand strong.

Therefore, it is possible to provide the light-emitting device, which ispollution-free, long-lasting, easy to produce, simple in structure, andstrong.

For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an oblique perspective view showing a stacked structure of alight-emitting device in accordance with one embodiment of the presentinvention.

FIG. 2 is an oblique perspective view showing a state in which anelectrostriction layer and a stress light-emitting layer in the stackedstructure of FIG. 1 are separated from each other.

FIG. 3 is an oblique perspective view showing a state in which thestress light-emitting layer in the stacked structure of FIG. 1 issandwiched between electrodes.

FIG. 4 is an oblique perspective view showing a state in which aplurality of the stacked structures of FIG. 1 are provided.

FIG. 5 is an oblique perspective view of a light-emitting device inaccordance with another embodiment of the present invention.

FIG. 6 is a graph showing a relationship between a mechanical stress anda stress-luminous intensity in the stacked structure of FIG. 1.

FIG. 7 is a graph showing a relationship between a strain ratio and thestress-luminous intensity in the stacked structure of FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment]

The following description deals with one embodiment of the presentinvention with reference to FIGS. 1 through 4.

As shown in FIG. 1, a stacked structure (light-emitting device) 1 inaccordance with one embodiment of the present invention includes anelectrostriction layer (electrostriction section) 2 and a stresslight-emitting layer (stress light-emitting section) 3.

The electrostriction layer 2 includes an electric inductive distortionmaterial whose crystals strain in response to an applied voltage. Theelectrostriction layer 2 has a thickness of about 11 m to 10 mm.Moreover, it is possible to use, as the electric inductive distortionmaterial, (i) an electrostriction ceramics material represented by 0.9MN-0.1PT ([Pb(Mg_(1/3)Nb_(2/3))_(0.9)Ti_(0.1)]O₃), (ii) a piezoelectricceramics material represented by PZT (Product Name: provided by CleviteCorp. (U.S.), (iii) a piezoelectric thin film vibrator materialrepresented by ZnO, or (iv) a high-polymer piezoelectric materialrepresented by a high-polymer material (polymer) or polyvinylidenefluoride (PVDF).

Pb(Mg_(1/3)Nb_(2/3))O₃, (Pb, Ba)(Zr, Ti)O₃, or (Pb, La)(Zr, Ti)O₃ can beused as the electrostriction ceramics material.

The piezoelectric ceramics material is indicated by a chemical formulaABO₃. Note that A and B are metallic elements, and each is composed ofone, or two or more replaceable element(s). Concrete examples of thepiezoelectric ceramics material are as follows.

Single-component type: BaTiO₃, PbTiO₃, crystal (SiO₂), LiNbO₃

Two-component type: PbTi_(0.48)Zr_(0.52)O₃

Three-component type: Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃,

-   -   —PbZrO₃,    -   Pb(Sb_(1/2)Nb_(2/3))O₃—PbTiO₃,    -   —PbZrO₃+MnO₂,    -   Pb(Mn_(1/3)Sb_(2/3))O₃—PbTiO₃,    -   —PbZrO₃,    -   Pb(Co_(1/3)Nb_(2/3))O₃—PbTiO₃,    -   —PbZrO₃

The piezoelectric thin film vibrator material is indicated by a chemicalformula MX. Note that M shows one, or two or more replaceable metallicelement(s), and X is any one of elements indicated by chemical symbolsN, O, S, and C. For example, concrete examples of the piezoelectric thinfilm vibrator material are a ZnO film, a CdS film, and an AlN film.

It is possible to use, as the high-polymer piezoelectric material, (i)an electret in which electric charges of positive and negativepolarities permanently appear respectively on both surfaces of ahigh-polymer film which is not subject to drawing process, and (ii) apiezoelectric film in which a polarization operation is carried out,under high temperature and high electric field, with respect to ahigh-polymer film which has been subject to the drawing process. Furtherconcrete examples of the high-polymer piezoelectric material arepolyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), and copolymerof vinylidene cyanide and vinyl acetate (P(VDCN/VAC)).

Note that, in the case where the electrostriction layer 2 deforms inresponse to an applied voltage, it is possible to select one from twotypes of combinations of the electrode and the electric inductivedistortion material, i.e., a simple deformation type or a flexuredeformation type. The simple deformation type is exemplified by mooneytype, cymbal type, or ultrasonic motor type. The flexure deformationtype is exemplified by monomorph, unimorph, or bimorph.

The stress light-emitting layer 3 includes a stress light-emittingmaterial which emits light in response to an applied mechanical energysuch as stress, vibration, friction, or the like. The stresslight-emitting layer 3 has a thickness of about 0.01 μm to 1 mm. Morespecifically, the stress light-emitting material includes, in aninorganic host material, at least one kind of metal ion as a luminescentcenter ion of the luminescence center. The metal ion indicates at leastone kind of metal ion of rare earth metal and transition metal whichemit the light when electrons excited by the mechanical energy move backtoward the ground state.

As the inorganic host material, oxide, sulfide, nitride, and carbide maybe used. A material indicated by the chemical formula xMO, yQ₂O₃, orzGO₂ is preferable as the oxide (M is Sr, Mg, Ba, or Zn; Q is Al, Ga, Y,or In; G is Ti, Zr, Si, or Sn). Note that, each of M, Q, and G can bepartially replaced with at least one kind of metal ion. Note also thateach of x, y, and z is an integer such as 0, 1, 2, 3, or the like.

Moreover, concrete examples of sulfide as the inorganic host materialare ZnS, CdS, MnS, MoS₃, and MnS₂. Concrete examples of nitride as theinorganic host material are AlN, GaN, InN, TaN, and the like, andconcrete examples of carbide are SiC, TiC, BC, and the like. Especially,aluminate or zinc sulfide is preferable as the inorganic host material.

It is preferable that a host material of the stress light-emittingmaterial is a material (i) which is composed of at least one kind ofaluminate having a non-stoichiometric composition, and (ii) which haslattice defect that causes electrons excited by the mechanical energy tocarry out luminescence when the electrons thus excited move back towardthe ground state. Furthermore, the above host material may include, asthe luminescent center ion of the luminescence center, at least one kindof metal ion selected from the rare earth metal ion and the transitionmetal ion. Note that, the non-stoichiometric composition indicates acomposition having a chemical composition formula which departs from astoichiometric chemical composition formula.

The rare earth metal ion selected as the luminescent center ion of theluminescence center is exemplified by Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or the like. The transition metal ionselected as the luminescent center ion of the luminescence center isexemplified by Ti, Zr, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ta, W, orthe like.

By thus including the luminescent center ion of the luminescence centerin the host material, it is possible to further increase a luminescenceintensity of the stress light-emitting layer 3. Especially, in the casewhere the host material is SrAl₂O₄, and when Sm, Eu, Gd, Tb, Dy or thelike is included in the luminescent center ion of the luminescencecenter, it is possible for the stress light-emitting layer 3 to emit thelight with strong luminescence intensity upon receipt of the stress.

Furthermore, it is preferable that the stress light-emitting layer 3 beprepared with the use of strontium aluminate as the stresslight-emitting material. Strontium aluminate also functions as theelectric inductive distortion material. As such, it is possible toutilize strontium aluminate when forming the electrostriction layer 2.That is, it is possible for the electrostriction layer 2 and the stresslight-emitting layer 3 to be made of a single material. This allows thesimplification of the manufacturing steps of the stacked structure 1. Itis also possible to reduce the cost for manufacturing the stackedstructure 1.

Moreover, the stacking of the electrostriction layer 2 and the stresslight-emitting layer 3 is carried out by PVD (Physical VaporDeposition), sputtering, evaporating, ion plating, or ion mixing.Further, CVD (Chemical Vapor Deposition), electrophoresis, coatingpyrolysis, spraying, or tape-casting may be used to stack theelectrostriction layer 2 and the stress light-emitting layer 3.Furthermore, the stacking of the electrostriction layer 2 and the stresslight-emitting layer 3 may be carried out, by applying the stresslight-emitting layer 3, with which an adhesive is mixed, onto theelectrostriction layer 2.

With the arrangement, when applying a voltage to the electrostrictionlayer 2 in the stacked structure 1 of the present embodiment, theelectric inductive distortion material deforms, so that theelectrostriction layer 2 also deforms. The deformation of theelectrostriction layer 2 causes an external force to act on the stresslight-emitting material of the stress light-emitting layer 3, therebyresulting in that the stress light-emitting layer 3 emits the light.That is, the applying of a voltage to the stacked structure 1 allows thestacked structure 1 to emit the light.

Note that, when the electrostriction layer 2 repeatedly applies thestress to the stress light-emitting layer 3, it is also possible to makethe stress light-emitting layer 3 flash on and off. Note that it isnecessary for the stress applied by the electrostriction layer 2 to bemuch smaller than the stress of an elastic limit of the stresslight-emitting layer 3. In concrete terms, it is preferable that thestress applied by the electrostriction layer 2 be 0.001% to 10% of thestress of the elastic limit of the stress light-emitting layer 3. Withthe stress, it is possible to avoid that any cracks or subsidiaryfractures occur in the stress light-emitting layer 3, even if the stressis applied repeatedly.

Note that it is not necessary that the indiscrete stacking of theelectrostriction layer 2 and the stress light-emitting layer 3 iscarried out. That is, the electrostriction layer 2 and the stresslight-emitting layer 3 may be separated from each other as shown in FIG.2. Note that it is necessary that a distance between theelectrostriction layer 2 and the stress light-emitting layer 3 isshorter than the maximal value of a possible deformation quantity of theelectrostriction layer 2.

In this case, when deforming the electrostriction layer 2 by applying avoltage, it is possible to instantaneously switch from a state in whichthe electrostriction layer 2 and the stress light-emitting layer 3contact with each other to a state in which the electrostriction layer 2and the stress light-emitting layer 3 do not contact with each other, orvice versa. That is, it is possible to instantaneously control lightingon/off of the stress light-emitting layer 3, by instantaneouslyswitching from a state in which the stress light-emitting layer 3 emitsthe light to a state in which the stress light-emitting layer 3 does notemit the light, or vice versa.

Moreover, the stress light-emitting layer 3 may be formed by mixing astress light-emitting material and a long phosphorescent phosphor. Itshould be noted that the long phosphorescent phosphors is a substancewhich stores incident light for a certain period of time. It is possibleto use SrAl₂O₄: Eu, Dy, aluminate, silicate, or Dy as the longphosphorescent phosphor, for example.

When thus forming the stress light-emitting layer 3 by mixing the stresslight-emitting material and the long phosphorescent phosphor, it ispossible to adjust the luminous intensity and a luminance persistencetime of the stress light-emitting layer 3.

Furthermore, as shown in FIG. 3, the stress light-emitting layer 3 maybe sandwiched between two electrodes 4 which are different from those(not shown) for applying a voltage to the electrostriction layer 2,while the stress light-emitting layer 3 is formed by mixing a stresslight-emitting material and an electroluminescence material. Note that,the electroluminescence material is a material which carries out theluminescence in response to an applied electric field.

There are various kinds of organic electroluminescence materials andinorganic electroluminescence materials. The inorganicelectroluminescence materials is exemplified by ZnGa₂O₄ family, ZnSfamily, MgGa₂O₄ family, or the like.

With the arrangement, it is possible to adjust the luminous intensity ofthe electroluminescence material by adjusting the voltage applied to theelectroluminescence material. This allows the adjustment of the luminousintensity of the stress light-emitting layer 3.

Moreover, as shown in FIG. 4, it may be possible to arrange a pluralityof the stacked structures 1 which are different in size. That is, it ispossible to arrange the stacked structures 1 so that a desired layout isrealized. Thus, in accordance with various purposes of use (which willbe described later) of the stacked structure 1, it is possible toarrange the stacked structures 1 with freely settable size, shape and/orlayout.

Moreover, the stacked structure 1 can be used in various manners, whichare explained below.

For example, it is possible to use the stacked structure 1 as thelight-emitting device. The electrostriction layer 2 and the stresslight-emitting layer 3 of the stacked structure 1 can be formed withoutusing materials, such as mercury used in the conventional fluorescentlamp, causing environmental problems. Therefore, it is possible to usethe stacked structure 1 as a light-emitting device causing noenvironmental problems.

Furthermore, the stacked structure 1 may be realized by a two-layerstructure of the electrostriction layer 2 and the stress light-emittinglayer 3. As such, it is possible for the stacked structure 1 to have asimpler and stronger structure, and to be easily fabricated, as comparedwith the conventional fluorescent character display tube having acomplicated structure.

Moreover, unlike the conventional incandescent lamp which emits thelight based on the heat radiation, the stacked structure 1 emits thelight by utilizing a nature in which the electrons carry out theluminescence when the electrons excited by the mechanical energy moveback toward the ground state. As such, the stacked structure 1 does notcause any heat rise. That is, the stacked structure 1 can be used as thelight-emitting device which has a long life, good luminous efficiency,and compact and strong structure.

Moreover, the stacked structure 1 can be used as a display device in adisplay.

More specifically, a plurality of stacked structures 1, whichrespectively include color filters in which layers carrying out lightemission of respective colors of R, G and B are alternately provided,are formed (i) so as to have the same size as or smaller than that ofLEDs which are used for the full-color screen display, and (ii) so as tobe arranged in a matrix manner. When changing the voltages to be appliedto the stacked structures 1 having the above arrangement, it is possibleto change external force applied to the stress light-emitting layers 3.That is, it is possible for each stacked structure to have a differentluminous intensity and a different luminous color.

Therefore, it is possible to carry out the image display with the samescreen size as the full-color screen using LEDs. Moreover, the stresslight-emitting layer 3 of the stacked structure 1 carries out planaremission. Therefore, it is possible to improve the image quality morethan the conventional full-color screen using LEDs which carry out thedot emission.

Moreover, when arranging the stacked structures 1 in a matrix manner asdescribed above, no space, which is hermetically sealed under vacuum, isformed, unlike the glass tube of the conventional CRT display. As such,it is possible to realize weight saving, and to improve crashworthy andheat resistance.

Moreover, it may be possible to turn on the respective stackedstructures 1 based on the same drive method (the simple matrix method,or the active matrix method) as that of the liquid crystal display,while using the stacked structures 1 as a light-emitting source(backlight) of the liquid crystal display. In this case, it is notnecessary to use the fluorescent tube, which uses mercury causingenvironmental problems, as the light-emitting source. Moreover, theelectrostriction layer 2 and the stress light-emitting layer 3 of thestacked structure 1 can be formed without using a material such asmercury causing environmental problems.

Therefore, when using the stacked structures 1 as the light-emittingsource of the liquid crystal display, it is possible to carry out theimage display, without causing any environmental problems, like theconventional liquid crystal display does.

Moreover, it is possible to use the stacked structure 1 as a stresssensor.

That is, in the case where the stacked structure 1 is provided on a wallsurface or the like of an architectural structure which is a measuringobject for the stress, the stress or vibration acted on the wall surfacealso acts on the stacked structure 1. Moreover, according to aluminescence characteristic, the greater the externally applied stressand vibration become, the stronger the luminous intensity of the stresslight-emitting material in the stress light-emitting layer 3 becomes.

As such, when measuring such a luminous characteristic of the stresslight-emitting layer 3 in advance, it is possible to visually recognizethe stress acted on the wall surface based on the luminescence intensityof the stress light-emitting layer 3. In this way, it is possible to usethe stacked structure 1 as the stress sensor.

Especially, the stress light-emitting layer 3 shows a distribution stateof the luminous intensity which varies depending on a distribution stateof the external force acted on the stress light-emitting layer 3. Thatis, in the case where the stacked structure 1 is used as the stresssensor, not only the stress acted on a specific point of the measuringobject but also the distribution state of the stress acted on themeasuring object can be visually recognized.

Moreover, the stacked structure 1 can be used as an embedded stresssensor. That is, the stacked structures 1 is embedded in the wallsurface or the like of the measuring object such as bridges, tunnels,roads, or architectural structures. In the circumstances, when detectingthe light, which is generated by the stress light-emitting layer 3, viaan optical fiber, it is possible to recognize the external force actedon the measuring object.

[Second Embodiment]

The following description deals with another embodiment of the presentinvention with reference to FIG. 5. Note that, in order to simplify theexplanation, members having the same functions as those shown in thefigures of the First Embodiment are denoted by the same referencenumerals and are not described repeatedly. Moreover, like the FirstEmbodiment, the present embodiment can combine various kinds of featuresdescribed in the First Embodiment.

As shown in FIG. 5, a light-emitting device 10 of the present embodimentincludes a plurality of electrostriction sticks (electrostrictionsection) 11 and a stress light-emitting layer (stress light-emittingsection) 12.

Like the electrostriction layer 2 of the First Embodiment, eachelectrostriction stick 11 includes an electric inductive distortionmaterial whose crystals strain in response to an applied voltage. Theelectrostriction sticks 11 are respectively formed so as to have acylindrical shape, and are arranged on the stress light-emitting layer12.

Like the stress light-emitting layer 3 of the First Embodiment, thestress light-emitting layer 12 includes a stress light-emittingmaterial, which emits the light in response to applied external force.The stress light-emitting layer 12 has a thickness of about 0.0 μm to 1mm.

With the above arrangement, when a voltage is applied to theelectrostriction sticks 11 in the light-emitting device 10 of thepresent embodiment, the electrostriction sticks 11 deform. Thedeformation of the electrostriction sticks 11 causes the external forceto act on the stress light-emitting layer 12. This allows the stresslight-emitting layer 12 to carry out the luminescence. Namely, theapplying of the voltage to the light-emitting device 10 allows thelight-emitting device 10 to emit the light.

Moreover, by applying a voltage to any one of the electrostrictionsticks 11, it is possible to apply the external force to part of thestress light-emitting layer 12. This allows a desired part of the stresslight-emitting layer 12 to emit the light.

EXAMPLE

The following description deals with a verified characteristic of theluminescence intensity of the stacked structure 1 in accordance with theFirst Embodiment of the present invention. Here, PMN (PbMgNbO₃), whichis aligned by the sputtering, is used as the electric inductivedistortion material in the electrostriction layer 2, and strontiumaluminate is used as the stress light-emitting material in the stresslight-emitting layer 3.

FIG. 6 is a graph showing a relationship, in the stacked structure 1 ofthe above structure, between the stress applied to the stresslight-emitting layer 3 and the luminous intensity. As shown in FIG. 6,it was clear that the luminous intensity depended on the stress, andthat the luminescence intensity increased with an increase in thestress.

Moreover, FIG. 7 is a graph showing a relationship between a strainratio of the electrostriction layer 2 and the luminous intensity. Asshown in FIG. 7, it was clear that the luminous intensity depended onthe strain ratio, and that the luminous intensity increased with anincrease in the strain ratio.

As described above, a light-emitting device of the present inventionincludes the electrostriction portion includes (i) an electrostrictionsection including an electric inductive distortion material whichdeforms in response to an applied voltage, and (ii) a stresslight-emitting section including a stress light-emitting material whichemits light in response to applied external force.

With the arrangement, the electric inductive distortion material and thestress light-emitting material can be formed without using materials,which cause the environmental problems, such as mercury which is used inthe conventional fluorescent tube. Furthermore, unlike the conventionalincandescent lamp, the light-emitting device of the present invention isnot arranged so as to emit the light based on the heat emission. Thelight-emitting device of the present invention emits the light byutilizing a nature in which the electrons carry out the luminescencewhen the electrons excited by the mechanical energy move back toward theground state. As such, the light-emitting device does not bring aboutthe heat rise caused by the light emission.

Therefore, it is possible to provide the light-emitting device which ispollution-free, long-lasting, easy to produce, simple in structure, andstrong.

Moreover, the light-emitting device of the present invention, in thelight-emitting device having the above structure, may be arranged sothat the electrostriction section and the stress light-emitting sectionare stacked.

With the arrangement, it is possible to surely transmit the deformationof the electrostriction section to the stress light-emitting section,and it is also possible to reduce the size of the light-emitting device.As such, when the light-emitting device is incorporated into otherdevices, it is easy to layout the light-emitting devices, and it ispossible to save spaces.

Alternatively, the light-emitting device of the present invention, inthe light-emitting device of the above structure, may be arranged sothat the electrostriction section and the stress light-emitting sectionare separated from each other.

With the above arrangement, when the electrostriction section deforms inresponse to an applied voltage, it is possible to instantaneously changefrom a state in which the electrostriction section and the stresslight-emitting section contact with each other to a state in which theelectrostriction section and the stress light-emitting section do notcontact with each other, or vice versa. That is, it is possible toinstantaneously change from a state in which the stress light-emittingsection emits the light to a state in which the stress light-emittingsection does not emit the light, or vice versa. As such, it is possibleto instantaneously control lighting on/off of the light-emitting device.

Alternatively, the light-emitting device of the present invention, inthe light-emitting device of the above structure, may be arranged sothat the stress light-emitting section is formed by mixing the stresslight-emitting material and the long phosphorescent phosphor.

With the arrangement, the light emitted by the stress light-emittingmaterial is temporarily stored by the long phosphorescent phosphor for apredetermined period of time. It should be noted that the longphosphorescent phosphor is a substance which can store the receivedlight for a predetermined period of time.

Therefore, it is possible to adjust the luminescence intensity and theluminance persistence time of the stress light-emitting section.

Alternatively, the light-emitting device of the present invention, inthe light-emitting device of the above structure, may be arranged sothat the stress light-emitting section is formed by mixing the stresslight-emitting material and the electroluminescence material, and issandwiched between electrodes which are different from electrodes forapplying a voltage to the electrostriction section.

With the arrangement, it is possible to adjust the luminescenceintensity of the electroluminescence material by adjusting the voltageapplied to the electroluminescence material. Note that theelectroluminescence material is a material which emits the light inresponse to an applied electric field. In this way, it is possible toadjust the luminescence intensity of the stress light-emitting section.

Alternatively, the light-emitting device of the present invention, inthe light-emitting device of the above structure, may be arranged sothat the electric inductive distortion material and the stresslight-emitting material are mixed. With the arrangement, it is possibleto integrally form the electrostriction portion and the stresslight-emitting portion. As such, it is possible to further downsize thelight-emitting device.

Moreover, the display device of the present invention is arranged so asto use any one of the light-emitting devices having the above respectivestructures.

With the arrangement, by forming the stress light-emitting section ofthe light-emitting device in a plan shape for example, it is possiblefor the light-emitting device of the present invention to emit theplanar light. As such, it is possible to improve the image quality morethan the conventional full-color screen using LEDs which carry out thedot emitting lights.

Moreover, it is possible to form an image display surface bycontinuously providing the stress light-emitting sections. Therefore,unlike the glass tube of the CRT display, it is not necessary to securea large space, which is hermetically sealed under vacuum, for the imagedisplay. As such, it is possible to improve the crashworthy and the heatresistance.

Furthermore, the electric inductive distortion material and the stresslight-emitting material in the light-emitting device of the presentinvention can be formed without using materials, which cause theenvironmental problems, such as mercury used in a light source of theconventional plasma display and the liquid crystal display.

Therefore, it is possible to carry out the image display without causingany environmental problems.

The stress sensor of the present invention is arranged so as to use anyone of the light-emitting devices of the above respective structures.

With the arrangement, it is possible to visually recognize the stressacted on the measuring object and the change ratio of the stress.Especially, the stress light-emitting section shows the distributionstate of the luminous intensity which varies depending on thedistribution state of the external force acted on the stresslight-emitting section and the vibration.

As such, not only the stress acted on a specific point of the measuringobject but also the distribution state of the stress acted on themeasuring object can be visually recognized.

Industrial Applicability

As described above, the light-emitting device of the present inventionis pollution-free, long-lasting, easy to produce, and is suitably usedas a display device or a stress sensor.

1. A light-emitting device, comprising: an electrostriction sectionincluding an electrostriction ceramics material as an electric inductivedistortion material which deforms in response to an applied voltage, anda stress light-emitting section including a stress light-emittingmaterial which emits light in response to applied external force,wherein the stress light-emitting section is formed by mixing the stresslight-emitting material and a long phosphorescent phosphor, and the longphosphorescent phosphor is SrAl₂O₄:Eu, aluminate, or silicate, andwherein the electric inductive distortion material and the stresslight-emitting material are mixed.
 2. A display device comprising thelight-emitting device as set forth in claim
 1. 3. A stress sensorcomprising the light-emitting device as set forth in claim 1, thelight-emitting device indicating a luminous intensity which variesdepending on a strain ratio.
 4. A light-emitting device, comprising: anelectrostriction section including an electric inductive distortionmaterial which deforms in response to an applied voltage, and a stresslight-emitting section including a stress light-emitting material whichemits light in response to applied external force, wherein the stresslight-emitting section is formed by mixing the stress light-emittingmaterial and a long phosphorescent phosphor, and the long phosphorescentphosphor is SrAl₂O₄:Eu, aluminate, or silicate, and wherein the electricinductive distortion material and the stress light-emitting material aremixed.
 5. A display device comprising the light-emitting device as setforth in claim
 4. 6. A stress sensor comprising the light-emittingdevice as set forth in claim 4, the light-emitting device indicating aluminous intensity which varies depending on a strain ratio.
 7. Alight-emitting device, comprising: an electrostriction section includingan electric inductive distortion material which deforms in response toan applied voltage, and a stress light-emitting section including astress light-emitting material which emits light in response to appliedexternal force, wherein the electric inductive distortion material andthe stress light-emitting material are mixed.
 8. A display devicecomprising the light-emitting device as set forth in claim
 7. 9. Astress sensor comprising the light-emitting device as set forth in claim7, the light-emitting device indicating a luminous intensity whichvaries depending on a strain ratio.